1. Technical Field of the Invention
The present invention relates to a turbofan engine. Additionally, the present invention relates to a structure which can be applied to a turbofan engine, and a fan rotor blade support structure for fixing a fan rotor blade for air introduction to a rotary disk to support this rotary disk.
2. Description of the Related Art
FIG. 1 is a schematic configuration diagram of a turbofan engine. As shown in this drawing, the turbofan engine 10 is provided with a fan rotor blade 1 for introducing air, a compressor 3 for compressing the introduced air, a combustor 5 for burning a fuel by the compressed air, a turbine 7 for driving the fan rotor blade 1 and the compressor 3 by a combustion gas of the combustor 5, an after burner 9 for afterburning to increase a thrust, a fuel nozzle (13), an ignition port (15), an outer duct (17) and the like. The fan rotor blade 1 is fixed to a rotary disk (not shown) which rotates integrally with the turbine 7.
The turbofan engine is a kind of a turbojet engine in which the size of the fan 1, which introduces air is increased, and a bypass ratio is increased. The bypass ratio corresponds to a flow rate ratio (bypass flow/core flow) between an air flow (a core flow) flowing into a core engine (the compressor 3, the combustor 5, and the turbine 7 described above) and a bypass flow bypassing them. There is an obtained effect of reducing the flow speed of an exhaust jet and lowering the noise level and fuel consumption, in accordance with an increase in the ratio.
[Problem 1]
However, in the above-described turbofan engine, when the bypass ratio is increased in order to attain a low fuel consumption and a low noise level, a first-stage fan rotor blade (an up-front fan blade) and the inner diameter of a casing surrounding the rotor blade are increased (refer to a two-dot chain line of FIG. 3, which will be described later), and the weight of the engine is increased (Problem 1). The details are as follows.
A first-stage fan rotor blade 1 of the structure embedded in a spinner 23 (refer to FIG. 1) of a turbofan engine requires a certain degree of hub/tip ratio (inlet hub radius/tip radius shown in FIG. 2: usually about 0.3) due to its embedded structure. Meanwhile, fan inlet area becomes narrow by the area equivalent to the inlet hub diameter.
Therefore, when the fan inlet area is increased in order to increase the bypass ratio, it is necessary to increase the fan diameter. In this case, since the inlet hub diameter also increases with the increase in the fan diameter in order to secure a hub/tip ratio of about 0.3, the weight of the engine will increase.
A technique for solving this Problem 1 is described in Patent Document 1.
In Patent Document 1, as shown in FIG. 3, a turbofan engine is provided with a first-stage fan rotor blade 27 for introducing air, and the spinner 23 which rotationally drives the first-stage fan rotor blade 27, and the spinner 23 has a spiral blade 29 which spirally extends radially outward from the Z axis, and sucks air from the front surface of the spinner to supply the air to the first-stage fan rotor blade 27.
In addition, in this drawing, reference numerals 31 and 31′ represent a casing inner diameter, and reference numeral 33 represents the flow of inflow air.
According to the configuration of Patent Document 1, the spinner 23 has the spiral blade 29 which spirally extends radially outward from the Z axis, and sucks air from the front surface of the spinner to supply the air to the first-stage fan rotor blade 27. Thus, air can be sucked even from the front surface of the spinner equivalent to the inlet hub diameter, and this air can be compressed and supplied to the first-stage fan rotor blade 27.
Accordingly, since the total area ahead of the engine becomes the air inflow area of the first-stage fan rotor blade 27, the fan diameter can be made small, and the suction flow rate of the first-stage fan rotor blade 27 can be increased. This can increase the bypass ratio, and reduce the engine weight. In addition, the first-stage fan rotor blade 27 and the spiral blade 29 are integrally formed to constitute the fan rotor blade.
Although Problem 1 can be solved by Patent Document 1 as described above, another problem 2 occurs when the following dovetail part and dovetail groove are used.
It is necessary to attach the fan rotor blade of the turbofan engine to the periphery of a disk (or spinner) which is rotationally driven by the turbine. Therefore, an attached part provided at the root of the fan rotor blade is attached to a fan rotor blade fixing part of the rotary disk. In the conventional technique, a dovetail part which extends in a front-back direction is provided at the root of the fan rotor blade as an attached part, and a dovetail groove is provided at the periphery of the disk as the fan rotor blade fixing part, and the dovetail part is made to fit into the dovetail groove.
In this conventional structure, the dovetail part and the dovetail groove are provided parallel to the axis of rotation Z-Z of the disk so that the centrifugal force which acts on the fan blade, does not generate an axial component force. Hereinafter, this structure is called “parallel dovetail structure”.
[Problem 2]
However, when an inner diameter of a doughnut-like flow passage where the fan blade is provided largely changes, and the parallel dovetail structure is adopted, it is necessary to reduce the diameters of the dovetail part and the dovetail groove to be equal to or less than the minimum diameter of the flow passage, and the length from the dovetail part to a blade tip at a radial outside end increases. As a result, there is a possibility that an excessive stress may be generated in the attached part (dovetail part) and the fan rotor blade fixing part (dovetail groove)(problem 2).
For this reason, a dovetail structure where the dovetail part and the dovetail groove, which are shown in FIG. 4, are inclined with respect to the axis of rotation is suggested (for example, Patent Document 2). In this drawing, reference numeral 35 represents a disk, reference numeral 37 represents a blade, 39 represents a dovetail, and reference numeral 41 represents a tab.
Hereinafter, this structure is called “inclined dovetail structure”.
[Problem 3]
However, when a fan rotor blade having a hub/tip ratio of 0 to 0.35 is applied to the inclined dovetail structure of Patent Document 2, the centrifugal force generated at a front part (part equivalent to the above-described spiral blade) of the fan rotor blade cannot be supported.
Thus, the inventor of the present application has studied the following configuration. That is, the inventor has studied that the front end of the root of the fan rotor blade is engaged and coupled with the spin cone fixed to the rotary disk on the upstream side of the rotary disk, and thereby, the centrifugal force which acts on the front part of the fan rotor blade with a small hub diameter is supported via the spin cone. (In addition, this configuration is the content which is not opened to the public on the filing date of the present application)
[Problem 4]
In this case, however, the centrifugal force of the front part is supported by the spin cone. Thus, an excessive stress may be locally generated in the spin cone (particularly, in an uppermost stream engaging part between the fan rotor blade and the spin cone) (Problem 4).    [Patent Document 1]    Japanese Patent Application Laid-Open Publication No. 2004-27854 “TURBOFAN ENGINE”    [Patent Document 2]    U.S. Pat. No. 6,764,282 “BLADE FOR TURBINE ENGINE”